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Amphicyonidae were named by Haeckel (1886) [also attributed to Trouessart 1885]. It was assigned to Carnivora by Sach and Heizmann (2001); to Arctoidea by Hunt (2001), Hunt (2002) and Hunt (2002); affirmed as Arctoidea by Zhai et al. (2003); affirmed to Arctoidea by Carroll (1988), Hunt (1998) and Wang et al. (2005); and to Caniformia by Morlo et al. (2007).[2][3][4]

Amphicyonids, often referred to as "bear dogs", crossed from Europe to North America during the Miocene epoch and are considered an Old World taxon. The earliest to appear is the (rather large) Ysengrinia (30—20 Mya), followed by Cynelos (24—7 Mya) and Amphicyon (23—5 Mya). These animals would have followed ungulates and other mammals to the New World for a period of about 7 million years. The New World amphicyonids of the subfamilies Daphoeninae (42-16 Mya) and Temnocyoninae (33-20 Mya) coexisted with the Old World counterparts.[5] Note that the (often similar looking) members of the family Hemicyonidae are also often called "bear-dogs" (although they are increasingly referred to as "dog-bears" to avoid confusion).

While amphicyonids have traditionally been viewed as closely related to ursids (bears), some evidence suggests they may instead be basal caniforms. (Hunt, 2004b). They were about as tall as the American black bear and were most likely ambushers because their legs were made for short, sudden bursts of speed. Bear dogs also nested their young in underground burrows.

During the early Miocene, a number of large amphicyonids migrated from Eurasia into North America. These taxa belong to the Old World amphicyonid subfamily Amphicyoninae. The earliest to appear is the large bear dog Ysengrinia Ginsburg, followed by Cynelos Jourdan, and then by Amphicyon. This influx of amphicyonines, accompanied by Old World ungulates and small mammals, indicates a prolonged interval (from 23 to 16.5 Mya) of faunal exchange between Asia and North America in the early Miocene, using the trans-Beringian route.[5] New World daphoenines (Daphoenodon, Borocyon) and temnocyonines coexisted with Old World amphicyonines (Ysengrinia, Amphicyon, Cynelos) 23.7-17.5 million years ago. These are the largest terrestrial carnivorans 50 to 200 kilograms (110 to 440 lb) to have evolved on the North American continent up to this time. The immigrant amphicyonines Ysengrinia, Cynelos and Amphicyon appear at 23, 19.2, and 18.8 Mya, respectively, and herald the beginning of a Eurasian amphicyonine migration into North America that continued into the mid-Miocene.[10]